Li-ion batteries (LIBs) have succeeded in powering small portable electric devices and are currently expanding to large scale applications (i. e. electric vehicles and grid-level energy storage systems). However, it is still debatable whether Li reserves can meet the increasing demand on such emerging applications. In fact, cost performance becomes the most important factor in the large scale applications. In this respect, K-ion batteries (KIBs) and Na-ion batteries (NIBs) are considered alternative energy storage systems due to the natural abundance of K and Na reserves. KIB technology is particularly interesting because K has a lower standard redox potential than Na in non-aqueous carbonate-based electrolytes that are commonly used for NIBs,^1-3 indicating that KIBs can potentially have a higher cell voltage than NIBs. More importantly, graphite, which has been used as a standard anode for LIBs because of low production cost as well as high density, can intercalate K ions reversibly while it cannot accommodate Na intercalation.^3,4

To realize practical KIBs, it is of primary importance to develop novel positive electrodes. In this study, we develop new cathode materials with layered-structure (i. e. K_xTMO₂, TM = Co and Mn)^{5, 6} for KIBs and investigate K-storage properties and underlying K-storage mechanism in them by in-situ diffraction and electrochemical characterization combined with theoretical first-principles calculations.

References

1. Eftekhari, A. et al. Potassium Secondary Batteries. ACS Appl. Mater. Sci., 9, 4404. (2016).

2. Marcus, Y. Thermodynamic functions of transfer of single ions from water to non-aqueous and mixed solvents: Part 3 - Standard potentials of selected electrodes. Pure and Applied Chemistry 57, 1129. (1985).

3. Komaba, S. et al. Potassium intercalation into graphite to realize high-voltage/high-power potassium-ion batteries and potassium-ion capacitors. Electrochem. Commun. 60, 172. (2015).

4. Jian, Z., et al. Carbon Electrodes for K-Ion Batteries. J. Am. Chem. Soc. 137, 11566. (2015).

5. Kim, H. et al. K-Ion Batteries Based on a P2-Type K_0.6CoO₂ Cathode. Adv. Energy Mater. 1700098. (2017)

6. Kim, H. et al. Investigation of potassium storage in layered P3-type K_0.5MnO₂ cathode. Adv. Mater. Under revision. (2017)